Europe, the art of the time was all drawn into its service, and thus it came to pass that bells having been, at a comparatively early period of the Christian era, introduced as an appendage to places of worship, their development, with all the art and science which the mediaeval workmen had at command, became almost inseparably connected with that of church architecture, and their sounds associated in an especial degree with church celebrations. The form of bell which may be said to have been perfected by mediæval bell-founders (for it has been accepted as a type upon which no essential or radical improvement can be made) is that shown in the following diagram, in which also the principal component parts of the bell are distinguished.
The elevation of the exterior of the bell explains itself; the section shows the relative thickness and shape of the metal; the thickest portion, the 'sound-bow,' A, against which the clapper strikes, is usually 1/12 th of the total diameter of the bell at the lip. The half-section marked No. 1 shows the old method of providing for the hanging of the bell and the attachment of the clapper; the loops called 'canons,' B, being cast on solid to receive the iron straps by which the bell is fixed to the stock, and the bolt, C, for attaching the clapper also cast solid on the inside of the bell. It is necessary that C should be well below the line of axis on which the bell swings, so as to describe an appreciable circle around the axis, otherwise there will be no leverage to drive the clapper, and it will not fly properly. The swing of the clapper is further ensured and accelerated by the small piece, D, called the 'flight,' cast on to the striking part to increase the impetus of the blow. Half-section No. 2 shows a method of hanging the bell and clapper recommended by Sir E. Beckett, and adopted in a good many instances by Mr. Taylor of Loughborough, in which canons are dispensed with, and a thick crown, E, is used with bolt holes through which the bell is bolted to the stock, and a larger hole in the centre through which the clapper-bolt is also fixed to the stock, instead of being cast on to the bell. The advantage of this plan is that the bell can easily be turned on the stock, the clapper-bolt (which is circular where it passes through the bell) remaining stationary, and thus the blow of the clapper can be directed against a new portion of the sound-bow, should the original striking place have become worn or show any tendency to crack.
The material of which bells are composed is a mixture of copper and tin, which in the old bells appear to have been used in the proportion of about 3 to 1. Modern experiment has given rise to the conclusion that, while this combination gave the best sound, and the proportion of tin might even be increased with advantage to the sound, this proportion represents the extreme amount of tin which can be used without the danger of rendering the metal brittle and liable to crack, and that in regard to this consideration a margin within that proportion of tin is safer. 22 of copper to 7 of tin was used for the Westminster bells in the Victoria Tower. Any considerably larger proportion of copper than this, on the other hand, has a tendency to render the metal too soft, and impair the brilliancy of its tone.
The conclusion that the special shape figured above, or something near it, is the best for a bell, has no basis that any one seems to know of except experience. It has been theoretically maintained that plain hemispherical bells ought to give the best and purest tone, but except on a small scale it is not found to be so; the result being either that the tone is very heavy and dead, or that when forced by hard striking it is unmusical and disagreeable to the ear. Sets of hemispherical bells have lately been made of larger size, and with more success than before; they require, however, to be fixed and struck, and not swung; their tone when not struck too heavily is not unpleasing, but quite inferior in power and brightness to that of a swung bell of the usual form. It is also to be noted, though this fact again is equally inexplicable, or at least unexplained, that large and small bells require somewhat differing shape and proportions to realise the best sound. That the proportionate thickness or weight of metal for producing the best results should be different for large and small bells, it is more easy to understand. Fora large bell, such as 6-feet diameter, experience seems to give a thickness of 1/12 of the diameter as the best proportion. Smaller bells will bear a somewhat greater proportionate thickness, and the proportionate thickness—that is to say, the proportionate weight of metal to the note prouced—is always increased in a large peal, from